 #include <stdio.h>
 int main()
{
 	int n;
 	double dividend,divisor;
 	double sum=0.0;
 	int i;
 	double t;
 	
 	scanf("%d",&n);
 	//n=20000;
 	dividend=2;
 	divisor=1;
 	for(i=1;i<=n;i++){
 		sum+=dividend/divisor;
 		t=dividend;
 		dividend=dividend+divisor;
 		divisor=t;
	 }
	 //printf("%f %f\n",dividend,divisor);
	 printf("%.2f\n",sum);
	 
	 return 0;
}
